Mutually beneficial relationships between vaginal bacteria may facilitate imbalances of vaginal microbiome
Bacterial vaginosis (BV) is an imbalance of the vaginal microbiome that can lead to adverse health outcomes, yet the mechanisms underlying infection-causing pathogen colonization are poorly understood. A study published in PLOS Biology by Amanda Lewis at University of California, San Diego, and colleagues suggests that mutually beneficial relationships between different species of vaginal bacteria may encourage growth of potentially harmful pathogens, challenging previous belief that the suitable living environment supporting pathogen colonization is created by the absence of healthy bacteria.
Approximately, 29% of women in the United States are affected by bacterial vaginosis, putting them at higher risk for adverse health outcomes such as preterm labor and amniotic fluid infections during pregnancy. To analyze interaction between bacterial communities and the ability of different bacteria to access required nutrients in an already-occupied microbiome, researchers conducted experiments in human vaginal specimens and mice. Using both in vitro and ex vivo mouse models, scientists inoculated mice vaginal communities with different bacteria cultures and compared the vaginal microbiome to a control group. After modeling bacterial interactions in mice, researchers then conducted similar experiments using human vaginal microbial communities obtained via vaginal swabs taken from twenty-one women, inoculated samples with Fusobacterium nucleatum, a bacterium linked with intrauterine infection and preterm birth.
The experiments led to the discovery that F. nucleatum does not act in a simple one-way relationship with other bacteria, but may engage in a mutually beneficial relationship, potentially encouraging dysbiosis (microbial imbalance) in susceptible vaginal communities. While the researchers were able to demonstrate that mutual benefit between bacteria species may promote pathogen colonization of the vagina and encourage features of vaginal dysbiosis, additional studies are needed to develop modes of prevention or treatment of BV in women. According to the authors, “These findings challenge the simplistic dogma that the mere absence of “healthy” lactobacilli is the sole mechanism that creates a permissive environment for pathogens during vaginal dysbiosis.”